i was a body man and i lived in mich i have fixed rust. i wish i did not .but the good way to fix it is with steel . but it can be fix with duraglas the duraglas will not rust it glass but it will rust around it . try not to grind it is thin and not much steel sand it with 36 on a d a and tap it low with a body hammer and work the filler up to the steel try to work it behined the steel so it is not thin at the edge of the good steel you want it low so you can fill it thick with duraglas. if there is nothing there big hole . you can use chicken wire and make the flare use to hold it poprivets THEY NEED TO BE LOW TO make shure the repair is low better than a 1/4. you need so this will be soild so no pinholes do not use body filler this is for finsh work and is not as water proof as the glass you can use a backer to so the glass will have some thing to stick to aluminfoil i hear it works good . work it out with a spreader if you use the foil work from the inside out set filler on foil and push it from back side use a shurform fie to it get were you want it alot less sanding keep file in paint thinner help keep it from pluging up. work the duraglas before it get to hard .I NEVER DID THIS BUT IT SHOULD WORK GOOD